Present day commercial lightwave systems use optical fibers to carry large amounts of multiplexed information over long distances from one location to another. Many transmission lines such as inter-office and intra-office links, local area networks (LAN) and metropolitan area networks (MAN) are optical and, therefore, the information that is being transmitted is carried over an optical fiber. A major advantage of transmitting information in optical form is the very large bandwidth and low losses associated with single mode optical fiber.
In a communication network, it is normally required that signals from many transmission lines be cross-connected or switched to other transmission lines to provide flexibility and to permit traffic from one transmission line to be rerouted to different destinations.
Various architectures that are being investigated for use in photonic switching in the time domain involve either fiber-loop or fiber-delay-line optical buffering. In an article in OFC/100C '93 Technical Digest by P. Gavignet-Mofin et al., there is disclosed a high-capacity optical buffer based on a set of fiber delay lines that realize in the photonic domain the equivalent of an electronic multibuffer shift register with variable delays for packet storage and time-switching applications in broad-band optical networks.
Until now, there has been no convenient approach to providing an optical delay line which can provide a variable delay and is economical to implement.